The Power in Willpower

Until recently, psychologists used to think of “willpower” as a metaphor, part of folk psychology having no relation to what actually happens in the head. The brain, seat of our decisions, wasn’t a muscle, after all. Self-control wasn’t “powered”, it was a cognitive thing, more like a computer than a car engine.

But new research from a lab at Florida State University is revealing that folk psychology was right all along. Self-control takes fuel — literally — and when we exercise it, resisting this or that temptation to misbehave, our fuel tank gets depleted, making subsequent efforts at self-control more difficult.

Florida State psychologist and APS Fellow Roy F. Baumeister and his colleagues Kathleen D. Vohs, University of Minnesota, and Dianne M. Tice, Florida State, showed this quite strikingly with an experiment using the Stroop task, a famous way of testing strength of self-control. Participants in this task are shown color words that are printed in different-colored ink (like the word red printed in blue font) and are told to name the color of the ink, not the word. Stress and other mentally depleting situations impair people’s ability to inhibit their first response (“red”) in favor of the correct one (“blue”); Baumeister found that when participants perform multiple self-control tasks like the Stroop test in a row, they do worse over time. Like a muscle, which gradually tires and eventually reaches exhaustion if strained to its limit, the ability to control ourselves wanes as it is exercised.

Moreover, the fuel that powers this ability turns out to be one of the same things that fuels our muscles: sugar, in the form of glucose.

The experimenters measured the blood glucose levels of participants before they engaged in another self-control task or a control task that did not involve self-control, and found that the self-control group (but not the controls) had suffered a depletion in glucose afterward. And in another experiment, two groups performed the Stroop task two times each, drinking one of two sweetened beverages in between. The control group got lemonade with Splenda, a sugar-free sweetener; the test group got lemonade sweetened with real sugar. The sugar group performed better than the Splenda group on their second Stroop test, presumably because their blood sugar had been replenished.

Now, if you’re watching your weight, you may already be scratching your head at the Catch-22 implied here. Sugar, the great white death, the 21st-century dieter’s antichrist, is also what helps you resist temptations … temptations like sugary drinks. Huh? Baumeister et al.’s findings are not a recipe for going out and consuming more sugar so that you can … well … resist sweets. For one thing, blood sugar does not stay with you but is constantly being depleted and consumed by the body.

But the research does suggest the possibility of psychological interventions for helping people achieve greater self-control. For one thing, again like muscles, self-control may be able to be strengthened through exercise. Results so far are inconsistent, Baumeister says, and some regimens work better than others, but he envisions that greater understanding of the biological and psychological underpinnings of our ability to control ourselves will have important real-world application for people in the self-control business, such as coaches, therapists, teachers, and parents.

To find out more about Baumeister’s research, see “The Strength Model of Self-Control” in the December issue of Current Directions in Psychological Science.